1. Field of the Invention
The present invention relates to a vehicle-mounted engine control apparatus that is capable of improving the air fuel ratio detection accuracy of an exhaust gas sensor used to properly control an air fuel ratio (a ratio of an amount of intake air to an amount of fuel injected) of a mixture in a vehicle-mounted engine. In particular, it relates to such a vehicle-mounted engine control apparatus that is improved to correct a change in individual variation of an exhaust gas sensor.
2. Description of the Related Art
In the past, in vehicle-mounted engine control apparatuses, there has been used an LAFS (Linear Air/Fuel Sensor) which is composed in combination of an oxygen concentration cell element and an oxygen pump element and which acts as an exhaust gas sensor for controlling an air fuel ratio (a ratio of an amount of intake air detected by an intake air amount sensor that measures or estimates an amount of intake air with respect to an amount of fuel supplied that is determined by a period of fuel injection) to a proper value in a negative feedback manner,
In addition, in a vehicle-mounted engine control apparatus using such a kind of exhaust gas sensor, various methods are adopted so as to prevent the deterioration of control precision resulting from a change in individual variation of the air fuel ratio detection characteristic of the exhaust gas sensor.
For example, as one example of a conventional vehicle-mounted engine control apparatus, there has been proposed a gas concentration detection apparatus having a gas sensor and a gas sensor connector (see, for example, a first patent document to be described later).
In the conventional apparatus described in the first patent document, the connector is connected through a cable to one end of a sensor main body through which a first pump current corresponding to the concentration of oxygen in a gas to be measured and a second pump current corresponding to the concentration of NOx in the gas flow.
In addition, the connector is provided, besides terminals for inputting and outputting signals to the sensor main body, with a label resistor that has a resistance value corresponding to the characteristic of the sensor main body (the relation between the oxygen concentration and the first pump current, and the relation between the NOx concentration and the second pump current), and a label signal output terminal connected to opposite ends of the label resistor.
In the above-mentioned construction, the characteristic of the sensor main body is specified by identifying the resistance value of the label resistor through the terminals, and the oxygen concentration and the NOx concentration are obtained from the detected values of the first and second pump currents with a high degree of precision based on the characteristic of the sensor main body thus specified.
On the other hand, as another conventional apparatus, there has been proposed a control apparatus for an internal combustion engine which is provided with a linear air fuel ratio sensor mounted on an exhaust pipe of an internal combustion engine for linearly measuring the air fuel ratio of an exhaust gas, an air fuel ratio control unit for correcting the air fuel ratio in the internal combustion engine in accordance with an output value of the linear air fuel ratio sensor, and a correction resistor for correcting an amount of error of the linear air fuel ratio sensor corresponding to an error between an output characteristic of the linear air fuel ratio sensor and a reference value (see, for example, a second patent document to be described later).
According to the conventional apparatus described in the second patent document, correction methods for the linear air fuel ratio sensor can be unified or standardized by correcting the output characteristic of the linear air fuel ratio sensor, so the number of kinds of linear air fuel ratio sensors is decreased and the amount of handling or dealing for each kind thereof can be increased, thus making it possible to achieve cost reductions.
In addition, by performing the reading of the error correction value at the time of initialization, there is no possibility of causing large damage to the sensors due to incorrect combinations, so the degree of freedom in combination of sensors and control circuits can be increased.
[First Patent Document]
Japanese patent application laid-open No. H11-281617 (FIGS. 2 and 4, paragraphs 0044 and 0054)
[Second Patent Document]
Japanese patent application laid-open No. 2002-256935 (FIGS. 2 and 25, and paragraphs 0030 and 0031